package main.java;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;

//HTTP 断点续传 demo（客户端测试工具：快车、迅雷）
@WebServlet(name = "ArcSyncHttpDownloadServlet", urlPatterns = "/down/ArcSyncHttpDownloadServlet")
public class ArcSyncHttpDownloadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    //记录已下载文件大小
    long pastLength = 0;
    //0：从头开始的全文下载；1：从某字节开始的下载（bytes=27000-）；2：从某字节开始到某字节结束的下载（bytes=27000-39000）
    int rangeSwitch = 0;
    //记录客户端需要下载的字节段的最后一个字节偏移量（比如bytes=27000-39000，则这个值是为39000）
    long toLength = 0;
    //客户端请求的字节总量
    long contentLength = 0;
    //记录客户端传来的形如“bytes=27000-”或者“bytes=27000-39000”的内容
    String rangeBytes = "";
    //负责读取数据
    RandomAccessFile randomAccessFile = null;
    //写出数据
    OutputStream outputStream = null;
    //缓冲
    OutputStream out = null;


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        //要下载的文件
        File downloadFile = new File("D:/BaiduNetdiskDownload/08_queue模拟.mp4");
        long fileLength = downloadFile.length();//记录文件大小
        System.out.println("fileLength：" + fileLength);
        //暂存容器
        byte bytes[] = new byte[1024];
        // 客户端请求的下载的文件块的开始字节
        if (request.getHeader("Range") != null) {
            response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);
            System.out.println("request.getHeader(\"Range\")=" + request.getHeader("Range"));
            rangeBytes = request.getHeader("Range").replaceAll("bytes=", "");
            int index = rangeBytes.indexOf('-');
            if (index == 1) {//bytes=969998336-
                rangeSwitch = 1;
                String temp0 = rangeBytes.substring(0, rangeBytes.indexOf('-'));
                String temp2 = rangeBytes.substring(rangeBytes.indexOf('-') + 1, rangeBytes.length());
                pastLength = Long.parseLong(temp0.trim());
                if ("".equals(temp2)) {
                    contentLength = fileLength - pastLength + 1;//客户端请求的是 969998336 之后的字节
                } else {
                    toLength = Long.parseLong(temp2);//bytes=1275856879-1275877358，到第 1275877358 个字节结束
                    contentLength = toLength - pastLength + 1;//客户端请求的是 1275856879-1275877358 之间的字节
                }
            } else {//bytes=1275856879-1275877358
                rangeSwitch = 2;
                String temp0 = rangeBytes.substring(0, rangeBytes.indexOf('-'));
                String temp2 = rangeBytes.substring(rangeBytes.indexOf('-') + 1, rangeBytes.length());
                pastLength = Long.parseLong(temp0.trim());//bytes=1275856879-1275877358，从第 1275856879 个字节开始下载
                toLength = Long.parseLong(temp2);//bytes=1275856879-1275877358，到第 1275877358 个字节结束
                contentLength = toLength - pastLength + 1;//客户端请求的是 1275856879-1275877358 之间的字节
            }
        } else {//从开始进行下载
            contentLength = fileLength;//客户端要求全文下载
        }

        /**
         * 如果设设置了Content-Length，则客户端会自动进行多线程下载。如果不希望支持多线程，则不要设置这个参数。
         * 响应的格式是:
         * Content-Length: [文件的总大小] - [客户端请求的下载的文件块的开始字节]
         * ServletActionContext.getResponse().setHeader("Content-Length",
         * new Long(file.length() - p).toString());
         */
        response.reset();
        //告诉客户端允许断点续传多线程连接下载,响应的格式是:Accept-Ranges: bytes
        response.setHeader("Accept-Ranges", "bytes");//如果是第一次下,还没有断点续传,状态是默认的 200,无需显式设置;响应的格式是:HTTP/1.1 200 OK
        if (pastLength != 0) {
        //不是从最开始下载, 响应的格式是: Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
            System.out.println("----------------------------不是从开始进行下载！服务器即将开始断点续传...");
            switch (rangeSwitch) {
                case 1: {//针对 bytes=27000- 的请求
                    String contentRange = new StringBuffer("bytes ").append(new Long(pastLength).toString()).append("-").append(new Long(fileLength - 1).toString()).append("/").append(new Long(fileLength).toString()).toString();
                    response.setHeader("Content-Range", contentRange);
                    break;
                }
                case 2: {//针对 bytes=27000-39000 的请求
                    String contentRange = rangeBytes + "/" + new Long(fileLength).toString();
                    response.setHeader("Content-Range", contentRange);
                    break;
                }
                default: {
                    break;
                }
            }
        } else {
            //是从开始下载
            System.out.println("----------------------------是从开始进行下载！");
        }

        try {
            response.addHeader("Content-Disposition", "attachment; filename=\"" + downloadFile.getName() + "\"");
            response.setContentType(CommonUtil.setContentType(downloadFile.getName()));// set the MIME type.
            response.addHeader("Content-Length", String.valueOf(contentLength));
            outputStream = response.getOutputStream();
            out = new BufferedOutputStream(outputStream);
            randomAccessFile = new RandomAccessFile(downloadFile, "r");
            try {
                switch (rangeSwitch) {
                    case 0: {//普通下载，或者从头开始的下载
                            //同1
                    }
                    case 1: {//针对 bytes=27000- 的请求
                        randomAccessFile.seek(pastLength);//形如 bytes=969998336- 的客户端请求，跳过 969998336 个字节
                        int n = 0;
                        while ((n = randomAccessFile.read(bytes, 0, 1024)) != -1) {
                            out.write(bytes, 0, n);
                        }
                        break;
                    }
                    case 2: {//针对 bytes=27000-39000 的请求
                        randomAccessFile.seek(pastLength - 1);//形如 bytes=1275856879-1275877358 的客户端请求，找到第 1275856879 个字节
                        int n = 0;
                        long readLength = 0;//记录已读字节数
                        while (readLength <= contentLength - 1024) {//大部分字节在这里读取
                            n = randomAccessFile.read(bytes, 0, 1024);
                            readLength += 1024;
                            out.write(bytes, 0, n);
                        }
                        if (readLength <= contentLength) {//余下的不足 1024 个字节在这里读取
                            n = randomAccessFile.read(bytes, 0, (int) (contentLength - readLength));
                            out.write(bytes, 0, n);
                        }
                        break;
                    }
                    default: {
                        break;
                    }
                }
                out.flush();
            } catch (IOException ie) {
            }
        } catch (Exception e) {
            System.err.println(e);
        } finally {
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    System.err.println(e);
                }
            }
            if (randomAccessFile != null) {
                try {
                    randomAccessFile.close();
                } catch (IOException e) {
                    System.err.println(e);
                }
            }
        }
    }
}